An optical sensor with the combination of colorimetric change of α-naphtholphthalein and internal reference luminescent dye for CO2 in water

A new optical CO2 sensor based on luminescence intensity changes of tetraphenylporphyrin (TPP) due to the absorption change of pH indicator dye (α-naphtholphthalein) with CO2 is developed and its CO2 sensing properties in pure water are investigated. The observed luminescence intensity from TPP at 650 nm increased with increasing the CO2 concentration in pure water. The ratio I100/I0, where I0 and I100 represent the detected luminescence intensities from a layer exposed to 100% argon and 100% CO2, respectively, that we takes the sensitivity of the sensor is estimated to be 430. The response times of the sensing film are 42.6 s for switching from argon to CO2, and 88.8 s for switching from CO2 to argon in pure water. The signal changes are fully reversible and no hysterisis is observed during the measurements.